The field of the invention is key operated switches for alarm systems and the invention is directed to such a switch which is designed to control two electrical circuits.
Alarm systems which use cylinder locks actuated by barrel keys are common especially for vehicles. The lock is of the so-called "Ace" type in which the key is a cylindrical instrument having varied recesses ground along its forward axial end adapted to cooperate with suitable pins in the receiving structure and characterized by the presence of a radial tooth which includes interior and exterior portions that must be inserted into the lock. The lock has a planar surface face plate and this plate presents an annular slot to its exterior with two radially outwardly extending short notches also in the face plate spaced about 90.degree. apart adapted to accommodate the tooth of the key during insertion and removal. The care of the lock cylinder also has a slot to be engaged by the interior part of the tooth.
In use, the key is inserted into the annular slot with the tooth aligned with one of the outer notches and the core notch and turned to bring the tooth and core notch into alignment with the second of the outer notches at which point the key can be removed. No other manipulation is possible. To place the switch in its former condition the key must be inserted with the tooth entering the second notch and reversed in rotation to the former position at which point the key can be removed.
This arrangement is common and well-known.
The invention herein concerns itself with two problems, namely constructing the electrical contacting means of the switch so that same will have perfect alignment in both conditions so that the key can be readily inserted and removed; and providing positive contact for the electrical contacting means.
In the process of achieving these ends a novel rotor and blade arrangement has been achieved which is efficient and quite simple.
The first mentioned problem arises because the limits of this type of switch must be controlled accurately. Some switches used detents which are not reliable, especially where the contact pressures are relatively high. This is true for vehicle alarm systems which often are connected into the starter control or into a main d.c. battery line. Other switches use expensive stop members requiring relatively high degrees of skill in the workmen assembling the same. In a small volume factory this makes the switches expensive.
The invention solves this quite simply by providing a stop member directly on opposite edges of the rotor adapted to engage with respective parts of the switch. Since each stop member is a simple sheet metal tab welded to the rotor or integral with the rotor, adjustment is facilitated by merely trimming the sheet metal of the tab without disassembling the switch.
The second problem arises because many alarm systems must be capable of being turned on and off a great many times and be capable of carrying considerable current. Especially in switches which are of the double pole double throw type, the electrical contact is established by a single flat blade engaging face to face with another flat blade. The contact thus established is not as good as could be achieved, for example, by the classical single blade robust knife switch which enters between a pair of juxtaposed contacts. There is no space for this latter type of switch in normal terminal boxes which are used for this type of alarm switch; such switches are normally used in circuits which carry high voltage and hence the juxtaposed contacts are not electrically independent of one another; such a structure would be considered too expensive for a switch of the type involved herein.
The invention solves this problem by a novel structure to be described which is very economical and yet efficient. It provides high current carrying capacity.
The prior art alarm switch which the invention is designed to supersede was likewise of a type to be mounted in a junction box of conventional construction. There were four contacts located 90.degree. apart and the rotor of the switch was coaxial with the lock cylinder and of elongate construction, comprising a metal member insulatedly mounted at its center on the end of the cylinder. The oppositely extending arms of the rotor each had a contact end which could bridge between each pair of diametrically disposed contacts. Each circuit was connected to a pair of such oppositely disposed contacts. The contact was established only as face to face and hence there was only that amount of pressure that could be achieved by the bent nature of the members establishing the contact coming into engagement with one another and being flexed by the physical engagement. The limits of rotation of the key were established by the cooperation between a segment of metal carried on the outer fixed shell of the cylinder and a washer with a segment-like tooth carried on the rotor. Adjustment involved proper placement of the washer relative to the shaft of the cylinder. Again the rotor of the switch had to be adjusted in its placement on the shaft of the cylinder to be able to move within the limits of the switch movement.